The availability of cDNA and genomic sequences for rat malic enzyme allowed us to probe for the molecular mechanism by which dehydroepiandrosterone increases the malic enzyme activity. Dehydroepiandrosterone, a naturally occurring steroid secreted from the adrenal, has been reported to decrease the body weight gain in rodents without suppressing food intake, and to stimulate malic enzyme activity in liver. In this report, we demonstrate that dehydroepiandrosterone induces hepatic malic enzyme activity by increasing the rate of transcription of the malic enzyme gene. This transcriptional activation of the malic enzyme gene is dose dependent, i.e., the treatment of euthyroid male rats with daily doses of 17.5 mg and 35 mg dehydroepiandrosterone per lOOg body weight for 7 days elevated the rate of malic enzyme gene transcription in liver 4-5 and 8-9 fold, respectively, above the basal levels. The levels of nuclear malic enzyme RNA, cytoplasmic malic enzyme mRNA, and enzyme activity were increased correspondingly. Malic enzyme stimulation by dehydroepiandrosterone was liver-specific, i.e., malic enzyme activity in brain, heart, kidney, and testis was unchanged. Thyroid hormone is required for the induction of hepatic malic enzyme activity by dehydroepiandrosterone since in hypothyroid animals dehydroepiandrosterone was without effect. However, malic enzyme stimulating effects of T3 and dehydroepiandrosterone are additive in euthyroid rat livers at both levels of gene transcription and enzyme activity.